Hi! A week ago I found a beautiful piece of driftwood at my LFS that I want to use in my tank. I soaked it in very hot water and when I checked the PH of the water after 24 hours my PH plummeted to 6 (my tap water ph starts off at about 8.4 but settles to about 7.2-7.6 after it gasses out for a few hours and that's what my tank's PH is). I've been soaking the piece for 7 days now since I bought it and changing out the water 1-2x per day and the PH is still dropping significantly.

The odd thing is that the water is clear: no brown water that would suggest tannins. Could the piece be leeching tannins even though the water isn't brown? If not, why is the PH dropping so much? Will it eventually stop or should I give up? From what I've read, DW shouldn't be dropping my PH this much this fast, so I'm not sure what's going on. A photo of the piece is below (I've since removed the "base" the piece came with thinking perhaps that was causing the PH drop but it isn't; the DW also sinks on its own without the base).

I do have a pice of DW in the tank now (purchased online) but am not sure what type of wood it is. It did leech tannins for a couple of days but then stopped and I did not notice any significant PH drops at the time (although I was fishless cycling when I put it in the tank but was testing PH regularly). My water is pretty soft; GH is 3 and KH is 2. Because of this I do have a pinch of crushed coral in the filter to keep the water buffered.

I also had an extra new filter lying around (a Tetra Whisper) so I added it to the tub with the DW last night and put some CC into it to try to mimic the tank's environment to see if the CC would keep the PH stable with the DW but 12 hours later the PH still fell to 6.8-7. I'd hate to rely on the CC to keep the water stable though.

The issue here is not really the wood, but the low GH and KH of the source water. I have the same issue. But with soft water fish, we are very lucky. There are other members with hard water that would love to have what we do coming out of the taps.

Back to the issue of the lowering pH. The natural biological processes in a balanced fish tank will naturally cause the pH to lower. CO2 is being produced by fish and plants respiration plus the breakdown of organics. CO2 creates carbonic acid, and the pH lowers accordingly as the acid increases. This is not in itself harmful, provided the fish are soft and acidic water fish. Although it can go too far.

Adding a calcareous mineral (dolomite, aragonite, crushed coral, crushed marble) will slowly add some calcium (and magnesium with some of these) to the water, increasing hardness and pH. I do the same in a couple of my tanks. The others i just let fall. It depends upon the fish species, some are fine in very acidic, some less so.

Wood releases tannins, and these contribute to the organics and acids. But this is usually minimal by comparison to the natural processes mentioned previously.

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian.[unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]

The issue here is not really the wood, but the low GH and KH of the source water. I have the same issue. But with soft water fish, we are very lucky. There are other members with hard water that would love to have what we do coming out of the taps.

Back to the issue of the lowering pH. The natural biological processes in a balanced fish tank will naturally cause the pH to lower. CO2 is being produced by fish and plants respiration plus the breakdown of organics. CO2 creates carbonic acid, and the pH lowers accordingly as the acid increases. This is not in itself harmful, provided the fish are soft and acidic water fish. Although it can go too far.

Adding a calcareous mineral (dolomite, aragonite, crushed coral, crushed marble) will slowly add some calcium (and magnesium with some of these) to the water, increasing hardness and pH. I do the same in a couple of my tanks. The others i just let fall. It depends upon the fish species, some are fine in very acidic, some less so.

Wood releases tannins, and these contribute to the organics and acids. But this is usually minimal by comparison to the natural processes mentioned previously.

Byron.

Thanks Byron! Yes my water is very soft! My tank's PH drops to about 7-7.2, sometimes 7.4-7.6, probably depending on what my municipality is doing to the water. Because of this I do have a small amount of crushed coral in my filter already to keep the water buffered and I do two 5-7 gal water changes weekly. As for the wood, I haven't added it to the tank yet which is probably a good thing given how low the PH dropped. I've added a larger amount of crushed coral to the filter I have running on the tub soaking the driftwood to see if that would stabilize the PH further. I may also try soaking the DW a while longer; perhaps I'm being impatient and a week isn't enough. I just don't want to chance the PH dropping significantly over a day or two with fish in the tank, so I'm hoping to get the water the DW is in more stable before I add it. Thanks for your advice and the link.

My fish probably wouldn't mind the lower PH; I'd just rather avoid fluctuations and if the PH in the tank fell too much then when doing a water change the PH would rise again significantly which worries me. Hopefully soaking the DW longer will help and if needed I can experiment with adding more coral to the filter. Thanks again.

Good news this morning I think. It's been 24 hours since I changed the water in the tub the DW is soaking in with an extra filter and some crushed coral and the PH matches my tank's PH at 7-7.2.

I'm going to let it soak a bit longer today and then change the water out again and let it soak for a couple of more days and keep testing PH. If after two days the PH is the same as the tank's PH, would it be safe to put the DW into the tank with the same amount of crushed coral that the DW is soaking with now? I'd keep testing PH daily of course to make sure it doesn't drop further. Or should I continue to soak it until the DW can hold PH on its own without relying on the coral?

Also the piece is quite large; is it OK to put it in with my fish in the tank if I'm careful and do it slowly? I don't want to stress them out too much. Perhaps I'd add some Stress Coat to the tank while I'm rearranging as well. I'm going to shoot for Wednesday as I have that day off assuming the PH stays stable. Thanks for your help!

I agree with all of the above unless livebearer's or other fishes being kept enjoy water with more hardness.
I have used crushed coral in the past, and found that when placed in the filter, in the path of water being returned to the tank, It can get covered over time,,,with silt,mulm,bacteria,algae,dirt,etc, and then becomes less effective at doin what you want it to do.
I might keep this material clean,or replaced with some regularity depending on it's condition.
If these are soft water fishes being kept, I would not worry bout the drop in pH which could be controlled if needed, by smaller ,more frequent water changes as opposed to single ,Larger water change. Opinion's vary.